Ammonia Stress Induces Transcriptional Expression Changes in the Mature Eggs of the Acipenser baerii

Ammonia is a key factor in the water, impacting the physiological functions of aquatic organisms. To explore the effect of ammonia stress on mature eggs, female <i>A. baerii</i> at the end of the fourth stage of ovarian development were subjected to varying ammonia concentrations (0 mg/L (control, C), 10 mg/L (low concentration, T1), and 50 mg/L (high concentration, T2)) for 96 h. After 96 h of stress, histological analysis revealed that the follicular membranes of group T1 remained intact and clear compared to group C, although the vacuole fusion had begun. In contrast, the T2 group exhibited ruptured follicular membranes and adhered yolk granules compared to the C group, indicating structural damage. Transcriptome analysis generated 97.89 Gb of clean data, with each sample yielding over 6.09 Gb. A total of 5576, 3719, and 9446 differentially expressed genes (DEG_S) were screened from T1 vs. C, T2 vs. C, and T2 vs. T1 comparisons, respectively. Gene Ontology analysis (GO) functional enrichment analysis showed that DEG_S were significantly enriched in multicellular organism processes (T1 vs. C), cell surface receptor signaling pathways (T2 vs. C), and immune system processes (T2 vs. T1) during biological processes. It indicates that ammonia exposure may enrich cellular components in the extracellular space, potentially disrupting the function of the extracellular matrix. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment indicated significant impacts on amino acid metabolism, particularly glutamate and arginine pathways, as well as key pathways involved in steroid biosynthesis and antioxidation. Weighted gene co-expression network analysis (WGCNA) revealed that a total of 26,369 DEGs were divided into 29 distinct modules, displaying obvious associations with their traits. In the T2 vs. C group, antioxidation-related genes such as <i>GST</i> and <i>GCLM</i> were significantly downregulated, and the expressions of key enzymes for steroid synthesis, such as <i>CYP11A1</i>, <i>CYP17</i>, and <i>CYP19A1</i> were suppressed, indicating that high ammonia nitrogen concentrations impair oocyte function by inducing oxidative stress and disrupting hormone synthesis. This study provides a comprehensive repertoire of candidate genes associated with ammonia stress in the mature egg of <i>A. baerii,</i> which will be useful for development of sturgeon breeding and reproduction.